selftests: filesystems: Add functional test for the abort file in fusectl

This patch add a simple functional test for the "abort" file
in fusectlfs (/sys/fs/fuse/connections/ID/abort).

A simple fuse daemon is added for testing.

Related discussion can be found in the link below.

Link: https://lore.kernel.org/all/CAOQ4uxjKFXOKQxPpxtS6G_nR0tpw95w0GiO68UcWg_OBhmSY=[e-mail]/
Signed-off-by: Chen Linxuan <[e-mail]>
Acked-by: Shuah Khan <[e-mail]>
Reviewed-by: Amir Goldstein <[e-mail]>
Signed-off-by: Miklos Szeredi <[e-mail]>

MAINTAINERS

···
 F:	Documentation/filesystems/fuse*
 F:	fs/fuse/
 F:	include/uapi/linux/fuse.h
+F:	tools/testing/selftests/filesystems/fuse/
 
 FUTEX SUBSYSTEM
 M:	Thomas Gleixner <[e-mail]>

tools/testing/selftests/Makefile

···
 TARGETS += filesystems/overlayfs
 TARGETS += filesystems/statmount
 TARGETS += filesystems/mount-notify
+TARGETS += filesystems/fuse
 TARGETS += firmware
 TARGETS += fpu
 TARGETS += ftrace

tools/testing/selftests/filesystems/fuse/.gitignore

···
+# SPDX-License-Identifier: GPL-2.0-only
+fuse_mnt
+fusectl_test

tools/testing/selftests/filesystems/fuse/Makefile

···
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+CFLAGS += -Wall -O2 -g $(KHDR_INCLUDES)
+
+TEST_GEN_PROGS := fusectl_test
+TEST_GEN_FILES := fuse_mnt
+
+include ../../lib.mk
+
+VAR_CFLAGS := $(shell pkg-config fuse --cflags 2>/dev/null)
+ifeq ($(VAR_CFLAGS),)
+VAR_CFLAGS := -D_FILE_OFFSET_BITS=64 -I/usr/include/fuse
+endif
+
+VAR_LDLIBS := $(shell pkg-config fuse --libs 2>/dev/null)
+ifeq ($(VAR_LDLIBS),)
+VAR_LDLIBS := -lfuse -pthread
+endif
+
+$(OUTPUT)/fuse_mnt: CFLAGS += $(VAR_CFLAGS)
+$(OUTPUT)/fuse_mnt: LDLIBS += $(VAR_LDLIBS)

tools/testing/selftests/filesystems/fuse/fuse_mnt.c

···
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fusectl test file-system
+ * Creates a simple FUSE filesystem with a single read-write file (/test)
+ */
+
+#define FUSE_USE_VERSION 26
+
+#include <fuse.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#define MAX(a, b) ((a) > (b) ? (a) : (b))
+
+static char *content;
+static size_t content_size = 0;
+static const char test_path[] = "/test";
+
+static int test_getattr(const char *path, struct stat *st)
+{
+	memset(st, 0, sizeof(*st));
+
+	if (!strcmp(path, "/")) {
+		st->st_mode = S_IFDIR | 0755;
+		st->st_nlink = 2;
+		return 0;
+	}
+
+	if (!strcmp(path, test_path)) {
+		st->st_mode = S_IFREG | 0664;
+		st->st_nlink = 1;
+		st->st_size = content_size;
+		return 0;
+	}
+
+	return -ENOENT;
+}
+
+static int test_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
+			off_t offset, struct fuse_file_info *fi)
+{
+	if (strcmp(path, "/"))
+		return -ENOENT;
+
+	filler(buf, ".", NULL, 0);
+	filler(buf, "..", NULL, 0);
+	filler(buf, test_path + 1, NULL, 0);
+
+	return 0;
+}
+
+static int test_open(const char *path, struct fuse_file_info *fi)
+{
+	if (strcmp(path, test_path))
+		return -ENOENT;
+
+	return 0;
+}
+
+static int test_read(const char *path, char *buf, size_t size, off_t offset,
+		     struct fuse_file_info *fi)
+{
+	if (strcmp(path, test_path) != 0)
+		return -ENOENT;
+
+	if (!content || content_size == 0)
+		return 0;
+
+	if (offset >= content_size)
+		return 0;
+
+	if (offset + size > content_size)
+		size = content_size - offset;
+
+	memcpy(buf, content + offset, size);
+
+	return size;
+}
+
+static int test_write(const char *path, const char *buf, size_t size,
+		      off_t offset, struct fuse_file_info *fi)
+{
+	size_t new_size;
+
+	if (strcmp(path, test_path) != 0)
+		return -ENOENT;
+
+	if(offset > content_size)
+		return -EINVAL;
+
+	new_size = MAX(offset + size, content_size);
+
+	if (new_size > content_size)
+		content = realloc(content, new_size);
+
+	content_size = new_size;
+
+	if (!content)
+		return -ENOMEM;
+
+	memcpy(content + offset, buf, size);
+
+	return size;
+}
+
+static int test_truncate(const char *path, off_t size)
+{
+	if (strcmp(path, test_path) != 0)
+		return -ENOENT;
+
+	if (size == 0) {
+		free(content);
+		content = NULL;
+		content_size = 0;
+		return 0;
+	}
+
+	content = realloc(content, size);
+
+	if (!content)
+		return -ENOMEM;
+
+	if (size > content_size)
+		memset(content + content_size, 0, size - content_size);
+
+	content_size = size;
+	return 0;
+}
+
+static struct fuse_operations memfd_ops = {
+	.getattr = test_getattr,
+	.readdir = test_readdir,
+	.open = test_open,
+	.read = test_read,
+	.write = test_write,
+	.truncate = test_truncate,
+};
+
+int main(int argc, char *argv[])
+{
+	return fuse_main(argc, argv, &memfd_ops, NULL);
+}

tools/testing/selftests/filesystems/fuse/fusectl_test.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+// Copyright (c) 2025 Chen Linxuan <[e-mail]>
+
+#define _GNU_SOURCE
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <dirent.h>
+#include <sched.h>
+#include <linux/limits.h>
+
+#include "../../kselftest_harness.h"
+
+#define FUSECTL_MOUNTPOINT "/sys/fs/fuse/connections"
+#define FUSE_MOUNTPOINT "/tmp/fuse_mnt_XXXXXX"
+#define FUSE_DEVICE "/dev/fuse"
+#define FUSECTL_TEST_VALUE "1"
+
+static void write_file(struct __test_metadata *const _metadata,
+		       const char *path, const char *val)
+{
+	int fd = open(path, O_WRONLY);
+	size_t len = strlen(val);
+
+	ASSERT_GE(fd, 0);
+	ASSERT_EQ(write(fd, val, len), len);
+	ASSERT_EQ(close(fd), 0);
+}
+
+FIXTURE(fusectl){
+	char fuse_mountpoint[sizeof(FUSE_MOUNTPOINT)];
+	int connection;
+};
+
+FIXTURE_SETUP(fusectl)
+{
+	const char *fuse_mnt_prog = "./fuse_mnt";
+	int status, pid;
+	struct stat statbuf;
+	uid_t uid = getuid();
+	gid_t gid = getgid();
+	char buf[32];
+
+	/* Setup userns */
+	ASSERT_EQ(unshare(CLONE_NEWNS|CLONE_NEWUSER), 0);
+	sprintf(buf, "0 %d 1", uid);
+	write_file(_metadata, "/proc/self/uid_map", buf);
+	write_file(_metadata, "/proc/self/setgroups", "deny");
+	sprintf(buf, "0 %d 1", gid);
+	write_file(_metadata, "/proc/self/gid_map", buf);
+	ASSERT_EQ(mount("", "/", NULL, MS_REC|MS_PRIVATE, NULL), 0);
+
+	strcpy(self->fuse_mountpoint, FUSE_MOUNTPOINT);
+
+	if (!mkdtemp(self->fuse_mountpoint))
+		SKIP(return,
+		     "Failed to create FUSE mountpoint %s",
+		     strerror(errno));
+
+	if (access(FUSECTL_MOUNTPOINT, F_OK))
+		SKIP(return,
+		     "FUSE control filesystem not mounted");
+
+	pid = fork();
+	if (pid < 0)
+		SKIP(return,
+		     "Failed to fork FUSE daemon process: %s",
+		     strerror(errno));
+
+	if (pid == 0) {
+		execlp(fuse_mnt_prog, fuse_mnt_prog, self->fuse_mountpoint, NULL);
+		exit(errno);
+	}
+
+	waitpid(pid, &status, 0);
+	if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+		SKIP(return,
+		     "Failed to start FUSE daemon %s",
+		     strerror(WEXITSTATUS(status)));
+	}
+
+	if (stat(self->fuse_mountpoint, &statbuf))
+		SKIP(return,
+		     "Failed to stat FUSE mountpoint %s",
+		     strerror(errno));
+
+	self->connection = statbuf.st_dev;
+}
+
+FIXTURE_TEARDOWN(fusectl)
+{
+	umount2(self->fuse_mountpoint, MNT_DETACH);
+	rmdir(self->fuse_mountpoint);
+}
+
+TEST_F(fusectl, abort)
+{
+	char path_buf[PATH_MAX];
+	int abort_fd, test_fd, ret;
+
+	sprintf(path_buf, "/sys/fs/fuse/connections/%d/abort", self->connection);
+
+	ASSERT_EQ(0, access(path_buf, F_OK));
+
+	abort_fd = open(path_buf, O_WRONLY);
+	ASSERT_GE(abort_fd, 0);
+
+	sprintf(path_buf, "%s/test", self->fuse_mountpoint);
+
+	test_fd = open(path_buf, O_RDWR);
+	ASSERT_GE(test_fd, 0);
+
+	ret = read(test_fd, path_buf, sizeof(path_buf));
+	ASSERT_EQ(ret, 0);
+
+	ret = write(test_fd, "test", sizeof("test"));
+	ASSERT_EQ(ret, sizeof("test"));
+
+	ret = lseek(test_fd, 0, SEEK_SET);
+	ASSERT_GE(ret, 0);
+
+	ret = write(abort_fd, FUSECTL_TEST_VALUE, sizeof(FUSECTL_TEST_VALUE));
+	ASSERT_GT(ret, 0);
+
+	close(abort_fd);
+
+	ret = read(test_fd, path_buf, sizeof(path_buf));
+	ASSERT_EQ(ret, -1);
+	ASSERT_EQ(errno, ENOTCONN);
+}
+
+TEST_HARNESS_MAIN